Control circuit and method of control for latching relay

ABSTRACT

Circuitry is designed to allow a change in potential level to cause latching or to cause unlatching of an electromechanical relay, with the change in potential level being amplified and supplied to the relay latching and unlatching circuit through a step-up transformer.

United States Patent u|13,562,602

[72] Inventors John G. Mlacak [50] Field ofSear-eh 317/154 Kanata,Ontario; Doron Cohen, Brampton, Ontario, Canada ['56] Cited [21] Appl.No. 690,354 UNITED STATES PATENTS' 1 Filed [kc-13,1967 2,982,887 5/1961Seeley 317/1s4x [45] Patented Feb. 9,1971 [73] Assignee NorthernElectric Company Limited f'm' f' M Mum Quebec Canada AssistantExaminer-William J. SmIth Attorney-Westell & Hanley [54] CONTROL CIRCUITAND METHOD OF CONTROL FOR LATCIIING RELAY ABSTRACT: Clrcurtry 15designed to allow a change In poten- Chin" nnwing tial level to causelatching or to cause unlatching of an elec- [52] [1.8. CI. 31 7/154,tromechanical relay, with the change in potential level being 317/ I54amplified and supplied to the relay latching and unlatching [51 Int.Cl..... lltllh 47/04 circuit through a step-up transformer.

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PATENTEU FEB 9197! INVEN'IUR.

JOHN G MLACAK WOHEN ATTORNEY CONTROL CIRCUIT AND METHODOF CONTROL FORLATCHING RELAY This invention relates to means and method forcontrolling the operating and releasing of an electromagnetic latchingrelay of the type which, when operated is adapted and connected to latchitself on through one of its main circuit connections and one of its owncontacts so that it may remain energized, in spite of the termination ofthe original energizing current. Such relay must be released byinterruption of the current flowing through the relay coil of thelatching circuit.

In control and switching systems it is quite often desirable that arelay may be actuated by a signal or pulse of limited duration and thatit will then remain in the state to which it is actuated after thetermination of the signal or pulse and until caused by anothercontrolsignal to release to its'original state.

Thus the relay used must have some sort of memory to memorize the lastcontrol instruction or in other words to remain in the state instructedafter the cessation of the instruction.

One approach to this has been the use of a magnetic latching relay. Thememory effect is achieved through the magnetic properties of a relaycore and the spring structure of such relays. The relay is designed sothat when pulsed by a predetermined voltage the relay will latch due toremanence magnetism in the core, resulting from the original pulse. Forrelease, a carefully timed pulse of the opposite sense is applied to therelay coil and the core is then demagnetized removing the holdingcoercive force. Considerable difficulties have been encountered in theoperation of such relays due to the necessity of careful timing of therelease pulse. lf the release pulse is too short the flux in the corewill change with the incidence of the pulse but with the removal of thepulse will return almost to its original state on the hysteresis curveleaving enough force for the relay to stay operated and the relaytherefore fails to release. If the release pulse is too long the stateof the core will travel to the other side of the hysteresis curve andthe relay will release but will subsequently reoperate so that sustainedrelease is not obtained.

Electronic latching has also been considered where an electronic circuitis attached to an electromagnetic relay to give it the latching propertybut such circuitry in large switching systems has been found to beextremely expensive and to render impractical many switching systems onthis basis.

The mode of latching with which this invention is concerned iselectrical latching which comprises an electromagnetic relay having oneof its contacts connected so that when the relay is operated it islatched on through its own contact. This mode of latching is of coursewell known and no claim is made herein to the development thereof.However, this invention concerns a circuit and a method of activatingsuch an electrical latching relay to allow for its use with switchingsystems and with control signals or changes in control signals oflimited magnitude and duration. The method for achieving latching orelectrical latching of the relay and the means therefor is alsoavailable for releasing the relay and means are provided herein forselectively controllable operate and release operations.

The control circuitry and method also permit easier and less complexdetection of the state (i.e. operated or released) of the relay.

It is an object of this invention to provide a control circuit adaptedto receive a change of amplitude in a control signal indicating aninstruction to latch the relay, and to magnify the effect of such changein amplitude to produce a pulse of sufficient duration and magnitude toachieve the latching operatron.

It is an object of this invention to provide similar circuitry to thatdescribed in the preceding paragraph for achieving the releasingoperation and, in a preferred embodiment to disclose means whereby withboth release and operate circuits means may be provided for preselectingone but not both of the release and operate operations whereby saidpreselection and the incidence of a timing pulse will cause the changeof signal amplitude in the circuit designed to achieve the desiredchange of relay state. Preferably the length of the timing pulse is usedto determine the length of the operate or release pulse with thecircuitry being designed to produce a pulse of the necessary magnitudeand shape to release or open the relay during the controlled pulseduration.

It is an object of this invention to provide means whereby a change inamplitude of a control signal (and by change in amplitude" we includethe situation where the change is to or from zero amplitude or to orfrom zero signal) indicating a desire to operate or to release therelay, is stepped up in a step-up transformer and applied as a pulse tothe relay as a potential alternatively:

a. tending to cause flow through the relay in the holding currentdirectionfor the latching operation;

b. tending to decrease flow through the relay in the holding currentdirectionfor the release operation.

it is an object of the invention to provide means whereby the change inthe control signal indicating a request to operate or a request torelease the relay is caused to change the state I of a transistor whosepower circuit thereupon alters the state of current flow through theprimary of a step-up transformer and where this change of state isapplied as a pulse to the relay in'a sense to (1) cause current flowtherethrough in the holding current sense and of sufficient magnitudeand duration to operate the relay or (2) reduce current flowtherethrough in the holding current sense to a sufficient degree tocause release of the relay.

It is an object of the invention to provide a method of operating orreleasing a latching electromagnetic relay comprising providing a changein signal level to indicate the request for operation or release, andcausing said change to alter the condition of current flow in theprimary of a step-up transformer and applying the pulse thereby producedin the secondary of the step-up transformer to a relay to initiate ordecrease the current therethrough in the holding current directiondepending on whether the operate or release opera- 1 10. It will beunderstood that the relay will have other contacts 'not shown whichperform the switching functions desired to be controlled by the relay. Aline 14 connects the control circuit to be described to the relaylatching circuit between relay 10 and resistance 12. The resistance 12not only limits the holding current, but, connected between line 14 andthe latching contact potential prevents control signals appearing alongline 14 from being shorted to ground before they affect the relayoperation. Four normally closed relay contacts 17 are shown in the line14. These have no intrinsic bearing on the operation of the inventionand should be considered as closed. Their only purpose is torespectively operate at the control of corresponding control relays (notshown) so that the opening of any of contacts 17 will preventapplication of a control signal to the latching relay at times when itis desired to inhibit the operation or release of relay 10 for reasonsextrinsic to the circuitry shown.

Line 14 is connected to B; which may be the same value as B, through aresistance 18, a condenser 20 and a resistance 22 in series to By whichmay be the same as B, but may be different in accord with therequirements of specific circuit design. The above components aredescribed out of logical sequence to clarify the fact that the mainpurpose of the circuitry shown to the left of this line indicated asline A-A is designed to operate the relay and the main purpose of thecircuit to the right of line A-A is designed to release the relay.

Considering, first, the circuit to the left side of line A-A a signalinput line is connected to 8+ supply line 102 through a diode 104 andresistance 106 in series with the diode poled to conduct when line 102is higher than the signal input on line 100. The junction betweenresistance 106 and diode 104 is connected through diode 108 to the baseof an NPN transistor 110 and the base is also connected to groundthrough a resistor 111. The diode 108 is poled to conduct when thepotential on the side thereof remote from the base of transistor 110 ishigher than at the base of the transistor. The connection between diode108 and the base of transistor 110 may be optionally connected to signalinputs 112 and 114 through diodes 117 and 118 respectively with each ofthe diodes being poled to conduct in the direction toward its respectiveinput.

it will be later seen that the operation of the invention will bedescribed ignoring the presence of the inputs 112 and 114, i.e.considering them as unconnected and later their significance in thecircuit will be discussed.

The collector of transistor 110 is connected to B+ line 102 throughresistor 113. The emitter of transistor 110 is connected to the base ofan NPN transistor 116 by a diode 119 with the diode poled to conductwhen the potential at the 110 emitter is higher than the 116 base. The116 base is also connected to ground through a resistor 120. Thecollector of transistor 116 is connected through resistance 122, zenerdiode 126 and a diode 128 in series to the base of transistor 110. Thezener diode 126 is poled to provide its design voltage drop topotentials higher at the collector of 116 than the base I of 110 and thediode 128 is poled to conduct for potentials higher in the same sense.The collector of transistor 116 is also Ct nnected through the primaryof a step-up transformer 130 to the 13+ line 102 and the dots on thetransformer windings indicate the-relative polarity of voltage changesbetween primary and secondary. One end of secondary of transformer 130is connected to B through resistance 22 and the connection between thesecondary and resistance 22 is connected to ground through a condenser134. The last named condenser acts as a ground to unwanted highfrequency noise appearing in the transformer secondary.

Connected in parallel with the secondary of transformer 130 is a seriescircuit comprising diode 136, resistance 138 and aparallel circuit withthe parallel circuit comprising the condenser 140 and the resistance 142in parallel. The diode 136 is poled to conduct when the potential at itsconnection to resistance 138 is higher than at its connection to thesecondary of transformer 130. The connection between the secondary oftransformer 130 and diode 136 (that is the end of the transformersecondary winding electrically remote from B is connected to line 14 (atits junction to line 16) through a resistor 144 and a condenser 146 inparallel; and then in series through a diode 148 with the diode beingpoled to conduct when the potential at the secondary of transformer 130is higher than the potential on line 14.

This is the circuit for operating," i.e. latching the relay and therewill now be described the counterpart circuit for releasing orunlatching the relay and it will be found that this circuitry issubstantially the same as that just described subject to the fact thatthe diode 248 is oppositely poled (relative to line 14) to itscounterpart 148 and that the relative polarities of primary andsecondary of transformer 230 is theopposite of such polarities for itscounterpart transformer 130 as indicated by the dots adjacent thetransformer winding.

Components in the circuit to the right of line A-A which are analogousto components in the circuit to the left thereof, will be givennumerical designations one hundred higher than the elements to whichthey are analogous.

Considering, now, the circuit to the right hand side of line A-A asignal input line 200 is connected to B+ supply line 102, through adiode 204 and resistance 206 in series with the diode poled to conductwhen line 102 is higher than the signal input on line 200. The junctionbetween resistance 206 and diode 204 is connected through diode 208 tothe base of an NPN transistor 210 and the base is also connected toground through a resistor 211. The diode 208 is poled to conduct whenthe potential on the side thereof remote from the base of transistor 210is higher than at the base of the transistor. The connection betweendiode 208 and the base of transistor 210 may be optionally connected tosignal inputs 212 and 214 through diodes 217 and 218 respectively witheach of the diodes being poled to conduct in the direction toward itsrespective input.

It will be later seen that the operation of the invention will bedescribed ignoring the presence ofthe inputs 212 and 214. i.e.considering them as unconnected and later their significance in thecircuit will be discussed.

The collector of transistor 210 is connected to B+ line 102 throughresistor 213. The emitter of transistor 210 is connected to the base ofan NPN transistor 216 by a diode 219 with the diode poled to conductwhen the potential at the 210 emitter is higher than the 216 base. The216 base is also connected to ground through a resistor 220. Thecollector of transistor 216 is connected through resistance 222, andzener diode 226 and a diode 228 in series to the base of transistor 210.The zener diode 226 is poled to provide its design voltage drop topotentials higher at the collector of 216 than the base of 210 and thediode 228 is poled to conduct for potentials higher on the same side.The collector of transistor 216 is also connected through the primary ofa step-up transformer 230 to the B+ line 102 and the dots on thetransformer indicate the relative polarity of voltage changes betweenprimary and secondary. It will be noted that the polarity is theopposite of that for transistor 130. One (the dotted) end of secondaryof transformer 230 is connected to B through resistance 22.

Connected in parallel with the secondary of transformer 230 is a seriescircuit comprising diode 236, resistance 238 and a parallel circuit withthe parallel circuit comprising the condenser 240 and the resistance 242in parallel. The diode 236 is poled to conduct when the potential at itsconnection to resistance 238 is lower than at its connection to thesecondary of transformer 230. The connection between the secondary oftransformer 230 and diode 236 is connected to line 14 (at its junctionto line 16) through a resistor 244 and a condenser 246 in parallel andthen in series with a diode 248 with the diode being poled to conductwhen the potential at the nondotted end of the secondary of transformer230 is lower than the potential at the junction of lines 14 and 16, thisbeing opposite to the polarity of diode 148 relative to the junction oflines 14 and 16.

Line 16 is connectable to a detector for detecting the state of relay 10and for reporting to the control circuitry. The detector forms no partof the present invention so is not described here, but may be of anywell known type of potential level detector designed to detect thedifference of potential on the line 14 between that existing in theconducting and nonconducting states of relay 10. One of the advantagesof the use of an electromagnetic latching relay with the control systemherein discussed is that the existing state of the relay may be easilydetected, at any time. With magnetic latching relays on the other handit has been found impractical to determine the relay state hence it hasbeen necessary with such relays to detect the transition between onestate and the other and this has been a more difficult and expensivepropositron.

The operation of the circuitry so far discussed will now be described.

Initially it will be assumed that terminals 112, 114, 212, 214 are opencircuited, and that the relay is deenergized. Transistor 110 would bebiased into conduction by the potential of its base obtained by thevoltage divider formed by resistances 106 and 111 between 8+ and ground,however with the biasing as shown, it is assumed that the quiescentstate of the signal on line is sufiiciently less positive than B+ thatthrough the action of diode 104, this potential applied across diode 108and resistance 111 biases transistor to nonconduction. Similarconditions apply on the release side of the circuitry. The bias whichwould be applied by the conduction from B+ through resistances 206 and211 to ground is not applied due to the design arrangement that thecontrol signal on line 200 shall be sufficiently less positive than B+that through the action of diode 204 transistor 210 is biased off.

It will be seen that when transistor 110 is nonconducting the base oftransistor 116 will have the same potential as the emitter and that thetransistor will be nonconducting, similarly when transistor 210 isnonconducting, there is no base-emitter potential on transistor 216 andthe latter is biased off.

The incidence of a positive signal on line 100 sufficiently positive tocause conduction in transistor 110 due to the greater potential actingacross diode 108 and resistor 111, acts as a command for the relay toclose. When such signal is received, conduction in transistor 110 biasesthe base of transistor 116 causing the latter transistor to conduct.Transistor 116 is preferably a transistor switch and the change to theconduction state is rapid. Conduction creates a surge of current throughthe primary of transformer 130 and drives the potential of the primaryremote from line 102 (the nondotted end) negative. The potential dropacross the primary is stepped up by the turns ratio to and in therelative polarity indicated by the dots. Since the nondotted end of thesecondary is tied to B the potential of the dotted end of the secondaryis driven positive by an amount determined by the magnitude of the inputsurge and the turns ratio. The turns ratio will therefore be calculatedto achieve the magnitude required for the operate pulse. The pulse isshaped during its passage through condenser 146. and resistance 144which may be of selected values to provide the desired shaping for thepulse. Preferably both C and R will be relatively large so that theinitial surge of the pulse is substantially all through the condenserand the shape of the pulse tends to be sharpened. The positive pulsepasses through diode 148 and the circuitry is designed so that the pulseshall be sufficiently positive relative to B,- to achieve energizationof the relay during the duration of the pulse passing through diode 148.1

The main problem of energizing relay is overcoming the inductance of itscoil and the pulse is therefore (in accord with design and its mode offormation) designed to have a large amplitude in its initial period anddecreasing amplitude.

thereafter. As a result of the application of the pulse, relay 10 isenergized (and it will be noted that the pulse causing such energizationcauses current flow through the relay in the same direction as thealternate holding current will be) closing its latching contact 10-1.When the pulse terminates therefore the relay will be held in operativeposition by the holding current from ground through closed contacts 101,resistance 12 with relay 10 to B,.

In relation to the magnitude of the actuating pulse, it will be notedthat some of this is dissipated through diode 248, resistance 244 andcondenser 246, in parallel, diode 236 resistance 238, condenser 240,resistance 242 (and to someextent through the secondary of transformer230) and then through resistance 22 to B The impedance of this lastdefined route is of course designed so that such dissipation will beminimal, having regard to the other necessary functions of thecomponents. However the pulse magnitude must be designed with suchdissipation inmind.

It is desirable that the pulse, which achieves the operation of relay 10shall terminate at the time the flow of holding current commences andfurther that the current created by the pulse at this time shall be asnear as possible to the holding current, so that there shall be as fewspikes as possible in the relay current during the transition. Thecurrent magnitude at termination is achieved by pulse shaping and thelength of the pulse is determined by termination of the command pulse online 100. It will be noted that while it might be thought that the pulsewould be terminated by the natural reverse swing in the transformer, ithas been found preferable to provide pulses of such duration that therelay would operate before the natural transformer reverse swing wouldcommence. lt has also been found preferable to dampen the transformer sothat there is in fact no material natural reverse swing of thetransformer. Hence the pulse is terminated by reverse swing caused bytermination of the command signal on line 100 rather than by the naturalreturn swing of the transformer. On termination of the command signalthe signal on line 100 goes negative stopping conduction in transistorwhich inturn cuts off conduction in transistor 116. This transitiontakes place somewhat more slowly than described since the resultantpositive swing of the nondotted end of the primary, causes a surgethrough the zener diode 126, maintaining transistor 110 and hencetransistor 116 conducting for a somewhat longer period than wouldotherwise be the case and. in effect making more gradual, the reversevoltage swing.

The reverse voltage swing in the primary of transformer creates asimilar swing in the secondary which causes the pulse applied across thediode 148 to'end when the potential approaches zero across diode 148.The further negative swing of the voltage at the transformer 130secondary does not affect the relay circuit due to the diode 148.

The reverse swing of the transformer secondary is dissipated throughdiode 136 and the circuit comprising resistance 138 and resistance 142and condenser 140 in parallel. The purpose of the resistance 138 andresistance 142 and condenser 140 in parallel is to limit the amount ofthe back-swing to measurable magnitudes on the one hand but not tolengthen its recovery time on the other. Diode 136 prevents theresistances and capacitances in parallel with the transformer secondaryfrom loading the secondary during the initial pulse.

' Resistance 144, in parallel with condenser 146 allows discharge of thecondenser between pulse applications. Resistance 142 performs the samefunction for condenser 140 between back-swings. The transformer 130 inaddition to its main step-up function acts to DC isolate the operatecontrol circuit from the relay preventing any false latching of therelay one way and preventing damage to the control circuitry by therelay potentials the other way.

A detector continuously connected-to line 16 will give a falseindication of .operating" just after the relay releases due tothereaction of the relay coil to the interruption of current,

and may give a false indication just after the relay has operated.Accordingly it will be desirable that detection means be designed(through means having no relation to the present invention) not todetect or to ignore detections made, during a predetermined period afteroperation or release of the relay.

The termination of the operate" operation concludes with transistors 110and 116 nonconducting.

The operation of the release circuit in response to a command pulse overline 200 is similar to that just described for the operate pulse andwill not be described as fully since the operation of the operate andrelease-circuits is substantially identical, except that componentvalues may be different due to a different desired magnitude or shapefor the release pulse to the relay.

When line 200 having been quiescent and negative, to prevent conductionin transistors 210 and 216, receives a positive signal (it being assumedthat the relay is then operated and contacts 10-1 are closed)ofsufficient magnitude to cause conduction in transistor 210, thisrepresents the command for the relay to release. Conduction intransistor 210 causes con duction in transistor 216 creating a surge ofcurrent in the primary and hence in the secondary of transformer 230which is positive toward the dot and negative away from the dot. Theprimary surge is stepped up in the secondary creating the negative pulseat the nondotted end of the secondary of transformer 230. This negativepulse is applied through resistance 244 and condenser 246 in parallel,through diode 248 to line 14. As the potential of line 14 is carriednegative by the pulse, current flow through relay 10 is reduced therebyuntil, as it goes below the holding minimum, the relay releases. Care istaken in circuit design that the negative swing of line 14 is not ofsufficient duration or magnitude that the relay will not be operatedthrough current flow through the relay in the opposite to the holdingcurrent direction. On the other hand the pulse from the secondary oftransformer 230 is made sufficiently large that dissipation in. thesecondary of transformer 11141 or through resistances 138, 142 andcondenser 140 through resistance 22 does not inhibit release of therelay by the pulse.

The above mentioned dissipation in the operate circuit during therelease operation, and the previously mentioned dissipation in therelease circuit during the operate operation, are merely design problemsand are small disadvantages compared to the advantage of being able toconnect both the operate and release circuits to the relay without thenecessity of interrupter relay contacts. Such relay contacts would addto the complexity and expense of the circuit and would require extradesign to avoid transient effects due to the closing and opening ofrelay contacts and would subject the circuit to the risk of mechanicalfailure.

The release circuitry has the same features as the operate. Thus thepulse emanating from the release circuitry through diode 248 isterminated not by the natural reverse swing of the transformer (which ispreferably damped out for all practical purposes) but rather after apredetermined positive signal duration, by the signal on line 200 goingnegative. It is noted that even if a reverse swing existed thecharacteristics of the transformer would be preferably designed so thatany reverse swing would occur after the termination of the pulse throughdiode 248 by the signal on line 200 going negative. Conduction is theninterrupted in transistor 210, interrupting conduction in transistor216, such interruption being rendered more gradual by the feedback fromthe transistor 216 through zener diode 226and diode 228. The positiveswing of the nondotted end of the primary of transformer 230 causes thenondotted end of its secondary to go positive, terminating the pulse tothe relay when the magnitude of the pulse emanating from the undottedend of transformer 230 secondary is more positive than line 14.

The circuitry in parallel with the secondary of transformer 230,comprising diode 246, resistance 238 condenser 140, and resistance 142serves the same purposes as the similar circuitry in the secondary oftransformer 130, with diode 246 being poled to prevent conduction in thesecondary of transformer 230 when the dotted end is positive relative tothe nondotted end.

Returning to the operate circuitry, terminal 112 may be operated in theuse of the circuitry above described, as a part larger control system.Terminal 112 may be connected to receive a control signal having twostates, a positive potential sufficient if connected to the base oftransistor 110 to bias transistor 110 into conduction and an alternatepotential sufficiently lower that transistor 110 will not conduct.Accordingly it will be noted that with the circuitry shown the positivesignal on terminal 112 is not sufficient to turn on transistor 110because of diode 117. On the other hand, withterminal 112 connected, apositive pulse on line 100, otherwise of sufficient magnitude to turn ontransistor 110, cannot do so unless 112 is in its positive state. Insuch an arrangement the pulse on line 100 may be provided at regularintervals, being ineffective when terminal 112 is not in its morepositive state and effective when 112 is in its more positive state. Thelatter condition, in combination with the positive pulse on line 100 byturning on transistor 110, creates the operate pulse for the relay.

It will be seen that terminal 114 has exactly the same effect asterminal 112 when connected to a source of control potentials, one highenough (although not connected to) bias transistor 110 into conduction,and one low enough to prevent conduction in transistor 110. When soconnected the higher potential on either or both terminals 112 and 114cannot cause an operate pulse which can only be caused by a coincidenceof positive signals on terminals 112 and 114 and line 100. Thus thesignal on line 114 maybe used as a redundancy check to prevent errors inoperation. Thus terminal 112 is used to indicate a request for anoperate pulse, terminal 114 is used to indicate thatthere is not at thesame time a request for a release pulse so that when 112 indicatesoperate 114 indicates not release then the next pulse on line 100 causesan operate pulse. lf conflicting commands were being given, when 112indicated operate" then 114 would be negative, i.e. release," and therelay would not be operated until 114 had altered in sign.

Similarly terminals 212 and 214 may be connected so that a release pulsemay only be when 212 is sufficiently positive to indicate release" and214 is sufficiently positive to indicate not operate."

It will be seen that when terminals 112, 114. 212. 214 are connected,then conflicting commands may not be given and the same pulses may besupplied on both line and 200 as indicated by the dotted connectingline300.

Relay contacts 17 are included toindicate that extrinsic controlcircuitry may command a large number of relays including four relayscorresponding to'the four contacts 17. and may operate to selectivelyclose or open contacts 17 in the circuit shown so that with suchcontrol, the circuit shown and other similar circuits affected by thesame control may be controlled to only operate as described where allfour contacts 17 in a circuit are closed.

It is noted that with the relay released B; may be different from B, byan amount sufficient to cause current flow (when no pulse is acting)either:

a. through elements 22, the secondary of 130, 144, 148. 14 and 10, inone polarity of B to 13,-; or

b. through elements 10, 14, 248, 244, the secondary of 230 and 22 in theother polarity of B to B,-.

As long as the difference of B and B, is insufficient to apply currentsof latching quantum'during the absence of a pulse and if the pulseproducing circuitry is designed with the values of B,, B and thequiescent current in mind; then this arrangement is considered to be andthe circuitry will operate in accord with the invention.

We claim:

1. Means for operating a latching electromagnetic relay connectable inseries with its latching contacts and a resistance between a firstpotential adjacentsaid relay and a second potential adjacent saidlatching contact said second potential being sufficiently-different fromthe first, to provide the necessary holding current for said relay,through said relay said resistance and said latching contact comprising:

a step-up transformer;

having one end of its secondary connected to a potential datum and theother end connected between saidrelay and said latching contact, saidresistance in series with said latching contact being connected betweenthe connection from said transformer secondary and said secondpotential;

means allowing current flow from said transformer secondary to saidrelay only when third potential created at said other end of saidtransformer secondary is in the same polarity relationship to theconnection point between said relay and said latching contact as saidsecond potential bears to said first potential; and

control means for altering the state of current flow in the primary ofsaid transformer between two states, at rates and to a degree that onalteration of said state in one a sense, a pulse of such third potentialis created of dura tion and magnitude to cause latching of said relay.

2. Means as claimed in claim 1 wherein said control means for alteringthe state of current flow comprises a transistor connected to provideone current flow state in said transformer primary when conducting andanother state when on nonconducting; and means for applying a controlsignal to the base of said transistor to switch said transistor on oroff.

3. Means as claimed in claim 1 wherein said control means for alteringthe state of current flow comprises: a transistor having its powercircuit connected in series with said transformer primary; means forconnecting a potential across said transistor switch and primary inseries, in a sense to conduct through said transistor switch, when theswitch is conducting;

and means for selectively applying and removing a biasing potential tosaid switch to initiate and interrupt conduction.

4. Means as claimed in claim 3 wherein said transformer is wired, andsaid means for allowing current flow in only one direction is poled, tocause said pulse when said transistor is switched on.

5. Means for releasing a latching electromagnetic relay connectable inseries with its latching contacts between a first potential adjacentsaid relay and a second potential adjacent said latching contact, saidsecond potential being sufficiently different from the first to providethe necessary holding cur rent for said relay through said relay' andsaid latching contact and a resistance in series therewith; comprising:

a step-up transformer;

having one end of its secondary connected to a potential datum and theother end connected between said relay and said latching contact beingconnected;

said resistance in series with said latching'contact between theconnection from said transformer secondary and said second potential;

means allowing current flow from said transformer secondary to saidrelay, only when'the third potential created at said other end of saidsecondary is in the same polarity relationship to the connection pointbetween said relay and said latching contact as said first potentialbears to said second potential; and

control means for altering the state of current flow in the primary ofsaid transformer at rates and tea degree, that on alteration of saidstate in one sense, a pulse of such third potential is createdofduration and magnitude to release said relay, but of insufiicientduration and magnitude to reoperate it.

6. Means as claimed in claim.5 wherein said control means for alteringthe state of current flow comprises a transistor,

connected to provide one current flow state in said transformer primarywhen conducting and another state when nonconducting; and means forapplying a control signal to the base of said transistor to switch saidtransistor on or off.

7. Means as claimed in claim 5 wherein said control means for alteringthe state of .current flow comprises: 'a transistor having its powercircuit connected in series with said transformer primary; means forconnecting a'potential across said transistor switch and primary inseries, in a sense to conduct through said transistor switch when'theswitch is conducting; and means for selectively applying and removing abiasing potential to said switch to initiate and interrupt conduction.

8. Means as claimed in claim 7 wherein said transformer is wired, andsaid means for allowing current flow in only one direction is poled, tocause said pulse when said transistor is' switched on.

sistor 9. Means for operating or releasing a latching electromagneticrelay connectable in series withits latching contactsand a resistancebetween a first potential adjacent said relay and a second potentialadjacent said latching contact. said second potential being sufficientlydifferent from the first. to provide the necessary holding current forsaid relay through said relay, said resistance and said latchingcontacts; comprising:

an operate circuit and a release circuit;

each of said circuits having a step-up transformer;

each said transformer having one end of its secondary connected to apotential datum and the other end connected between said relay and saidlatchingcontact; said series resistance being connected between bothsaid transformer secondary connections and said second potential;

the connection from one transformer secondary allowing current flow onlyaway from said transformer secondary toward said relay;

and the connection from the other transformer secondary allowing currentflow only toward said transformer secondary from said relay;

control means associated with the primary of each transformer forselectively altering the state of the current flow in the primary ofsaid transformer between two states; and stationary means for preventingsubstantial current flow from pulse provided at either one of saidtransformer secondaries in the circuit of the other of said transformerseconda es. r V i v v Ill Means as c aimedin claim? wherein saidcontrolmeans for altering the state of current flow comprises: a tranhaving itspower circuit connected in seri e s yvith each transformer primary;means for connecting a potential across said transistor switch andprimary in series, in a sense to conduct through said transistorswitchwhen the latter is conducting; and means for selectively applyingand removing a biasing potential to said switch to initiate andinterrupt conduction therein.

ll. Means as claimed in claim 10 wherein each said transformer is wiredand each said means for allowingcurrent flow in only one direction ispoled to cause a pulse to pass through the respective one way currentflow means associated with a transformer secondary, when the transistorassociated with the primary of the same transformer is turned on.

1. Means for operating a latching electromagnetic relay connectable inseries with its latching contacts and a resistance between a firstpotential adjacent said relay and a second potential adjacent saidlatching contact said second potential being sufficiently different fromthe first, to provide the necessary holding current for said relay,through said relay said resistance and said latching contact comprising:a step-up transformer; having one end of its secondary connected to apotential datum and the other end connected between said relay and saidlatching contact, said resistance in series with said latching contactbeing connected between the connection from said transformer secondaryand said second potential; means allowing current flow from saidtransformer secondary to said relay only when third potential created atsaid other end of said transformer secondary is in the same polarityrelationship to the connection point between said relay and saidlatching contact as said second potential bears to said first potential;and control means for altering the state of current flow in the primaryof said transformer between two states, at rates and to a degree that onalteration of said state in one sense, a pulse of such third potentialis created of duration and magnitude to cause latching of said relay. 2.Means as claimed in claim 1 wherein said control means for altering thestate of current flow comprises a transistor connected to provide onecurrent flow state in said transformer primary when conducting andanother state when on nonconducting; and means for applying a controlsignal to the base of said transistor to switch said transistor on oroff.
 3. Means as claimed in claim 1 wherein said control means foraltering the state of current flow comprises: a transistor having itspower circuit connected in series with said transformer primary; meansfor connecting a potential across said transistor switch and primary inseries, in a sense to conduct through said transistor switch, when theswitch is conducting; and means for selectively applying and removing abiasing potential to said switch to initiate and interrupt conduction.4. Means as claimed in claim 3 wherein said transformer is wired, andsaid means for allowing current flow in only one direction is poled, tocause said pulse when said transistor is switched on.
 5. Means forreleasing a latching electromagnetic relay connectable in series withits latching contacts between a first potential adjacent said relay anda second potential adjacent said latching contact, said second potentialbeing sufficiently different from the first to provide the necessaryholding current for said relay through said relay and said latchingcontact and a resistance in series therewith; comprising: a step-uptransformer; having one end of its secondary connected to a potentialdatum and the other end connected between said relay and said latchingcontact being connected; said resistance in series with said latchingcontact between the connection from said transformer secondary and saidsecond potential; means allowing current flow from said transformersecondary to said relay, only when the third potential created at saidother end of said secondary is in the same polarity relationship to theconnection point between said relay and said latching contact as saidfirst potential bears to said second potential; and control means foraltering the state of current flow in the primary of said transformer atrates and to a degree, that on alteration of said state in one sense, apulse of such third potential is created of duration and magnitude torelease said relay, but of insufficient duration and magnitude toreoperate it.
 6. Means as claimed in claim 5 wherein said control meansfor altering the state of current flow comprises a transistor connectedto provide one current flow state in said transformer primary whenconducting and another state when nonconducting; and means for applyinga control signal to the base of said transistor to switch saidtransistor on or off.
 7. Means as claimed in claim 5 wherein saidcontrol means for altering the state of current flow comprises: atransistor having its power circuit connected in series with saidtransformer primary; means for connecting a potential across saidtransistor switch and primary in series, in a sense to conduct throughsaid transistor switch when the switch is conducting; and means forselectively applying and removing a biasing potential to said switch toinitiate and interrupt conduction.
 8. Means as claimed in claim 7wherein said transformer is wired, and said means for allowing currentflow in only one direction is poled, to cause said pulse when saidtransistor is switched on.
 9. Means for operating or releasing alatching electromagnetic relay connectable in series with its latchingcontacts and a resistance between a first potential adjacent said relayand a second potential adjacent said latching contact, said secondpotential being sufficiently different from the first, to provide a thenecessary holding current for said relay through said relay, saidresistance and said latching contacts; comprising: an operate circuitand a release circuit; each of said circuits having a step-uptransformer; each said transformer having one end of its secondaryconnected to a potential datum and the other end connected between saidrelay and said latching contact; said series resistance being connectedbetween both said transformer secondary connections and said secondpotential; the connection from one transformer secondary allowingcurrent flow only away from said transformer secondary toward saidrelay; and the connection from the other transformer secondary allowingcurrent flow only toward said transformer secondary from said relay;control means associated with the primary of each transformer forselectively altering the state of the current flow in the primary ofsaid transformer between two states; and stationary means for preventingsubstantial current flow from pulse provided at either one of saidtransformer secondaries in the circuit of the other said transformersecondaries.
 10. Means as claimed in claim 9 wherein said control meansfor altering the state of current flow comprises; comprises: atransistor having its power circuit connected in series with eachtransformer primary; means for connecting a potential across saidtransistor switch and primary in series, in a sense to conduct throughsaid transistor switch when the latter is conducting; and means forselectively applying and removing a biasing potential to said switch toinitiate and interrupt conduction therein.
 11. Means as claimed in claim10 wherein each said transformer is wired and each said means forallowing current flow in only one direction is poled to cause a pulse topass through the respective one way current flow means associated with atransformer secondary, when the transistor associated with the primaryof the same transformer is turned on.